a) Technical Field
The present invention relates to the field of treating water containing potentially undesirable living organisms, and more particularly to a composition and a method for treating ship ballast water to kill or eliminate harmful prokaryotic or eukaryotic aquatic organisms.
b) Background Art
It has long been recognized that invasions by non-native aquatic species are increasingly common worldwide in coastal habitats. Transportation and introduction of non-indigenous species in ship ballast water has created substantial economic and environmental impact throughout the world. Global shipping, which moves 80% of the world's commodities and is fundamental to world trade, inadvertently transports many aquatic organisms.
Ballast water transport of alien species has been determined in several countries to be a national environmental conservation issue of the highest priority. For example, zebra mussels, toxic dinoflagellates, stinging jellyfish, and numerous fish and invertebrate species have all been transported into new habitats via ship ballast water. These introductions have caused broad environmental impact, have had tremendous economic impacts in remedial actions, and have focused government legislators on the development of controls that will have serious ramifications to both commercial and military shipping.
While filtration of the ballast water may seem to be a logical solution, the volume and rate of filtration (to 25,000 cubic meters/hr), coupled with occasional heavy silt loads, make this option difficult to achieve. Other methods, including the use of biocides, ozonation, ultraviolet treatment, chemical deoxygenation, magnetic fields and sonication, have been tested, each with operational or economic shortcomings.
For example, tests conducted on the use of biocides and herbicides show that the treatment of ballast water with these agents would both be expensive and cause unpredictable pollution and destruction to the local ecological environment upon discharge of the treated ballast. Further, it has been found that when sub-optimal concentrations of the biocides and herbicides are used, the numbers of organisms in the ballast water may actually increase.
Heat sterilization of ballast water with steam or engine heat would also be expensive and also has the problem of causing accelerated corrosion due to the increased ballast water temperature.
The current best technology for attempting to cure the problem of transporting undesirable organisms is to require ships to exchange, in mid-ocean or on the high seas, the original local ballast water with the saline, open ocean sea water. However, such an exchange of ballast water on the high seas is potentially extremely hazardous, especially, for large cargo ships and tankers, and in any event has been shown not to be fully effective in removing all microorganisms and higher living organisms from a ship's hold.
This mid-ocean ballast exchange is usually (but not always) safe when the space in which the water is being exchanged is small enough so as not to create a dangerous instability or structural stress condition during the water-pumping process for effecting the exchange; for example, such a ballast exchange usually (but not always) is safe when dealing with specialized ballast tanks or other similar small spaces because of the low ratio of the weight of the involved water with the overall weight of the ship, and because of the ability of the load bearing strength of the ship to accommodate a temporarily empty “small” specialized ballast tank.
However, it is often required that cargo holds or large ballast tanks be filled with water so that the ship's center of gravity is lowered during a voyage when no cargo is carried. Under these conditions, one or more cargo holds or tanks are often filled with ballast water. Because these holds or tanks contain very large spaces, they must be kept either completely full or completely empty so that interior wave action does not develop. Thus, if ballast exchange were attempted from such a large space and the ship encountered heavy seas in the middle of the pumping process, then there could develop inside the space a wave action which could destabilize the ship and create a very dangerous condition.
One relatively recent approach that has been proposed to reduce introduction or propagation of undesirable organisms in ship ballast water is deoxygenating by nitrogenous treatment. While reduction of survivorship of organisms and microorganisms is observed in ship ballast, there is always need of important sources of nitrogen on the ships. The system generating the necessary nitrogen is money and energy consuming, without considering the important time needed for maintenance of the systems. The arrangements that must be taken to meet the normative security rules are also often very constraining.
In considering the state of the art mentioned above, it is still highly desirable to be provided with new approaches for control of unwanted biological material in transportation and relocation of large volumes of water.